Again Idk if the pistons were made for open chamber or not. I didnt build it. Ill snap a few pics later on when I get off work. I really havent had any time to look over anything at this point. Just took a few minutes yesterday morning to pull all the pushrods out. If I have time this week I should be able to get a better idea of the problem.

Whelp after looking into it 5 of the exhaust pushrods were bent & one intake. That's checking them on the work bench. I'll know 100% tomorrow when I get to work & roll them on the granite slab. Further investigation has concluded that the exhaust valves are hitting the pistons. Later in the week I'll do a leak down & go from there. I'm speechless at this point.

Makes total sense. Easy thing to confuse BB pistons and reliefs - one version even uses two different part numbers, one for each side of the block (I found this during a search for the L78 proper piston part numbers). Betcha the builder never checked the valve to piston clearance during the build - you're probably lucky it didn't mangle it worse. Sounds like a cam change would be in the works -

Hate it happened, but glad it did it now rather than strand you somewhere, or grenade it -

Wow ,you know who built it ( 8 years ago) If the above is the case, no way that motor was broke in as claimed. Solid lifter would have presented when rotating on the stand. Once the hydraulic ones pumped up...can't imagine the other 3 exhaust didn't suffer. No use pondering on this , once you open it up, you'll discover the mix matching of parts. Sorry man.

Like I posted ,I've wiped pushrods out with no piston or valve damage. Other than the PITA of pulling the engine , may not be a lot of damage to your wallet.

Oh, cut open your oil filter to see what's in there for metal particles. (if the lobes got ground off ,guess where they are at) You know this Darrell, posting for the 100's who happen on this site and don't.

Yeah knowing how I am; Ill be pulling the motor and doing a complete teardown, inspection & rebuild. Sucks but I will feel better about it knowing I built the engine...

Also, when I was using the Snap-on bore scope I noticed metallic on the tops of pistons (which is expected) along with scoring on the cylinder wall on at least one cylinder. Needless to say I could chew nails at this point. But I am already running combos through my head on how I want to build it.

I know how you feel. Long story short, I didn't have an engine balanced when it was inspected and installed. Then I had my throttle stick and I pulled a couple of rocker arm studs out, luckily no damage. In the process of tear-down and inspection I found the crank to be bad and of course then the bearings. I had to hone and then clean the block out about 10 times to get all the grit out. If I would have just made sure it was right before I got in a hurry to get the motor in, I would have been driving it for the last year and a half.

Again Idk if the pistons were made for open chamber or not. I didnt build it. Ill snap a few pics later on when I get off work. I really havent had any time to look over anything at this point. Just took a few minutes yesterday morning to pull all the pushrods out. If I have time this week I should be able to get a better idea of the problem.